Phase-locked loop

ABSTRACT

A phase lock circuit has a signal path to which a phase comparator, a loop filter and a voltage control oscillator are connected in series, the phase comparator being adapted to compare the phase of an input signal V IN  with the phase in the output signal of the voltage control oscillator and to output its result of comparison, the loop filter being adapted to receive the output signal of the phase comparator and to output a DC voltage; the voltage control oscillator being adapted to control the output oscillation frequency depending on the DC output voltage of the loop filter, the phase lock circuit further comprising voltage tracking means for adding, to the voltage of the signal path, a signal causing the average voltage in the output voltage of the phase comparator to coincide with a predetermined reference voltage, whereby the voltage tracking means can enlarge the lock range in the phase lock circuit.

FIELD OF THE INVENTION

[0001] The present invention relates to a phase lock circuit(phase-locked loop circuit) usable in optical communication and radio communication devices and particularly to a phase lock circuit which can surely continue the lock at an ultra-high frequency band (which is substantially equal to or higher than 5 GHz) whereat clock and data recovery(CDR) and phase-frequency comparison circuits cannot be used since they have narrower lock ranges and tend to create unlocking, even if the aged deterioration of parts, temperature change, variation of supply voltage and other undesirable events occur.

BACKGROUND OF THE ART

[0002]FIG. 14 is a block diagram of a phase lock circuit(phase-locked loop circuit) PS111 according to the prior art.

[0003] The phase lock circuit PS111 comprises a phase comparator 1 i, a loop filter 2 i, a voltage control oscillator(voltage-controlled oscillator) 3 i, a signal input terminal 7 i and a signal output terminal 9 i. The phase comparator 1 i is formed by an EXOR circuit.

[0004]FIG. 15 (1) shows the waveform of an input signal 7 i (V_(IN)); FIG. 15 (2) shows the waveform of the output from the voltage control oscillator 3 i; FIG. 15 (3) shows the waveform of the output from the phase comparator 1 i; and FIG. 15 (4) shows the waveform of the output from the loop filter 2 i.

[0005] It is assumed therein that the duty ratio of the pulse of the input signal 7 i (V_(IN)) shown in FIG. 15 (1) and the pulse of the voltage control oscillator 3 i shown in FIG. 15 (2) is equal to 50%.

[0006] As shown in FIG. 15 (3), the duty ratio in the phase comparator 1 i is determined by the leading edge timing in the pulse of the input signal 7 i (V_(IN)) shown in FIG. 15 (1) and the leading edge timing in the output pulse of the voltage control oscillator 3 i shown in FIG. 15 (2).

[0007] The output level of the loop filter 2 i shown in FIG. 15 (4) is determined by the duty ratio of the phase comparator 1 i shown in FIG. 15 (3) while the oscillation frequency of the voltage control oscillator 3 i is determined by the output level of the loop filter 2 i.

[0008] Namely, in the phase lock circuit PS111 of the prior art shown in FIG. 14, the phase difference between the pulse of the input signal 7 i (V_(IN)) shown in FIG. 15 (1) and the output pulse of the voltage control oscillator 3 i shown in FIG. 15 (2) determine the oscillation frequency of the voltage control oscillator 3 i.

[0009] When the phase lock circuit PS111 is in its locked state, the above-mentioned phase difference is determined such that the frequency (or bit rate) of the input signal 7 i (V_(IN)) shown in FIG. 15 (1) coincides with the output frequency of the voltage control oscillator 3 i.

[0010]FIG. 15 (1) shows a case where the phase difference is equal to 125 while FIG. 15 (2) shows another case where the phase difference is equal to 90.

[0011] If the control coefficient of the voltage control oscillator 3 i (or ratio between the control voltage and the output frequency) is positive and when the right-side graphs (II) of FIG. 15 are reference, the left-side graphs (I) of FIG. 15 illustrate that the frequency (or bit rate) of the input signal 7 i (V_(IN)) is higher.

[0012]FIG. 16 shows changes in the output voltage of the loop filter 2 i when the frequency (or bit rate) of the input signal 7 i (V_(IN)) is changed.

[0013] The phase lock circuit PS111 is in its locked state in the middle area of the lock range (or area between the lower and upper ends of the lock range).

[0014] As the frequency (or bit rate) of the input signal 7 i (V_(IN)) varies, the aforementioned phase difference also varies to change the duty ratio in the output signal of the phase comparator 1 i and the output voltage of the loop filter 2 i.

[0015] However, the duty ratio has the lower limit (0%) and the upper limit (100%). In other words, the limits of the duty ratio in the output of the phase comparator 1 i exist in the upper and lower ends of the lock range.

[0016] If the phase lock circuit is to be applied to the communication system, the parameters of the phase lock circuit (e.g., loop filter bandwidth and gain) must be determined such that the specification of a frequency synthesizer such as phase noise characteristic or the specification of CDR such as jitter tolerance will be satisfied. This raises a problem in that a sufficiently broad lock range cannot be provided.

[0017] If the lock range is not sufficiently broad and when a drift occurs in the oscillation frequency due to various environmental variations such as the aged deterioration of the voltage control oscillator (VCO), temperature change and supply voltage variation, there is raised a problem in that the lock cannot be held. In addition, the oscillation frequency of the voltage control oscillator must accurately be pre-regulated on shipment.

[0018] If the phase lock circuit additionally includes a retraction circuit (see Japanese Patent Application No. Hei 8-130468), it raises still another problem in that the lock range would extremely be reduced.

[0019] The retraction circuit is added to the phase lock circuit for enlarging the pull-in range therein. When the phase lock circuit is in its unlock state, the retraction circuit inputs a scanning signal into the voltage control oscillator to change the oscillation frequency greatly. As the oscillation frequency approaches to the frequency of the input signal, the retraction circuit retracts the phase lock circuit. Thereafter, the locked state of the phase lock circuit is detected and the phase lock circuit is controlled to hold the voltage in the scanning signal, thereby maintaining the locked state thereof.

[0020] However, the retraction circuit does not have a function of lock-range enlargement. If the retraction circuit retracts the oscillation frequency at the end of the lock range, the substantial lock range (or minimum distance between the retracting frequency and the lock range end) will extremely be reduced. This raises a further problem in that the locked state will not be maintained stable.

[0021] An object of the present invention is provide a phase lock circuit which can provide a very broad lock range even if the lock range is reduced by regulating the parameters of the phase lock circuit to satisfy the jitter tolerance and so on or even if the lock range is substantially reduced by adding the retraction circuit into the phase lock circuit.

[0022]FIG. 17 is a block diagram of another phase lock circuit PS112 according to the prior art, into which a retraction circuit according to the prior art is added.

[0023] The phase lock circuit PS112 comprises a phase comparator 1 n, a loop filter 2 n, a voltage control oscillator 3 n, a signal input terminal 7 n, a signal output terminal 9 n, a lock detector 21 n, an additional loop or retraction circuit FS1 and an adder 6. The phase comparator in, loop filter 2 n and voltage control oscillator 3 n together define the main body of the phase lock circuit. The retraction circuit FS1 comprises a pulse generator 23 n, a counting circuit 24 n and a D/A converter 25 n, as shown in Japanese Patent Application No. Hei 8-130468.

[0024] The retraction circuit FS1 is added to the phase lock circuit for enlarging the pull-in range therein. When the phase lock circuit is its unlocked state, the retraction circuit FS1 inputs a scanning signal to the voltage control oscillator 3 n to change the oscillation frequency thereof greatly. As the oscillation frequency approaches to the frequency of the input signal, the retraction circuit FS1 retracts the phase lock circuit. Thereafter, the locked state of the phase lock circuit is detected. At this time, the retraction circuit controls the phase lock circuit to hold the voltage of the scanning signal and to maintain the locked state of the phase lock circuit.

[0025]FIG. 18 shows waveforms in the primary parts of the phase lock circuit PS112 into which the retraction circuit is added.

[0026]FIG. 18 (1) shows the waveform in the output signal of the loop filter 2 n; FIG. 18 (2) shows the waveform in the output signal of the lock detector 21 n; FIG. 18 (3) shows the waveform in the output signal of the pulse generator 23 n; and FIG. 18 (4) shows the waveform in the output signal of the D/A converter 25 n.

[0027] In the initial stage of the time chart (left side about a dotted line), the phase lock circuit PS211 is in its unlocked state which is discriminated by the lock detector 21 n. The pulse generator 23 n produces a pulse. In association with this, the counting circuit 24 n varies its count while the D/A converter 3 n changes its output voltage in a stepwise manner. The output, voltage of the D/A converter 25 n varies the oscillation frequency of the voltage control oscillator 3 n. As the oscillation frequency approaches to the frequency of the input signal, the phase lock circuit is retracted. Thereafter, the lock detector 21 n discriminates the locked state of the phase lock circuit and the pulse generator 23 n is stopped. The counting circuit 24 n maintains its count constant while the D/A converter 25 n maintains its output voltage constant to hold the locked state of the phase lock circuit. As a result, the pull-in range can be enlarged within a range in which the oscillation frequency of the voltage control oscillator 3 n is variable.

[0028] On the other hand, there exists the output voltage range of the D/A converter 25 n in which the locked state of the phase lock circuit can be maintained (see FIG. 18 (4)). However, the actuation of the lead-in(retraction) circuit not necessarily causes the output signal of the D/A converter 25 n to occur at a position near the center of this voltage range. If the locked state is maintained at a position near the lower (or upper) limit of the lock range as shown in FIG. 18 (4), the substantial lock range (or minimum distance between the retracting frequency and the lock range end) will extremely be reduced. In such a case, the locked state cannot be maintained stable due to the subsequent environmental variation such as supply voltage variation, temperature change, jitter input).

[0029] Even if the phase lock circuit is unlocked, it will again be retracted by the lead-in(retraction) circuit. However, this raises further problems in that a spurious radiation occurs during a period between the unlocking and the completion of re-retraction (if the phase lock circuit is applied to a frequency synthesizer) and in that the data is lost (if the phase lock circuit is applied to CDR).

[0030] The present invention is to provide a phase lock circuit which can enlarge the lock range thereof and maintain the locked state stable, even though the above-mentioned lead-in(retraction) circuit is added to the phase lock circuit.

DISCLOSURE OF THE INVENTION

[0031] The present invention provides a phase lock circuit(phase-locked loop circuit) comprising a signal path connected in series with a phase comparator, a loop filter and a voltage control oscillator(voltage-controlled oscillator), said phase comparator being adapted to compare the phase of an input signal with the phase in the output signal of said voltage control oscillator and to output its result of comparison, said loop filter being adapted to receive the output signal of said phase comparator and to output a DC voltage; said voltage control oscillator being adapted to control the output oscillation frequency depending on the DC output voltage of said loop filter, said phase lock circuit further comprising voltage tracking means for adding, to the voltage of said signal path, a signal causing the average voltage in the output voltage of said phase comparator to coincide with a predetermined reference voltage, whereby said voltage tracking means can enlarge the lock range in said phase lock circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a block diagram of a phase lock circuit PS1 according to the first embodiment of the present invention.

[0033]FIG. 2 illustrates the dependency of the average voltage in the output signal of a phase comparator 1 a on the frequency of an input signal 7 a (V_(IN)) when the phase lock circuit PS1 of the first embodiment is in its locked state.

[0034]FIG. 3 shows signal waveforms in the primary parts of the phase lock circuit PS1 when signals having such characteristics (i) and (ii) as shown in FIG. 2 are inputted.

[0035]FIG. 4 is a block diagram of another phase lock circuit PS2 according to the second embodiment of the present invention.

[0036]FIG. 5 is a block diagram of still another phase lock circuit PS3 according to the third embodiment of the present invention.

[0037]FIG. 6 shows signal waveforms in the primary parts of the phase lock circuit PS3.

[0038]FIG. 7 is a block diagram of still another phase lock circuit PS4 according to the fourth embodiment of the present invention.

[0039]FIG. 8 is a block diagram of still another phase lock circuit PS5 according to the fifth embodiment of the present invention.

[0040]FIG. 9 is a block diagram of still another phase lock circuit PS6 according to the sixth embodiment of the present invention.

[0041]FIG. 10 is a circuit diagram of a differential integrator.

[0042]FIG. 11 is a block diagram of still another phase lock circuit PS7 according to the seventh embodiment of the present invention.

[0043]FIG. 12 shows waveforms in the primary parts of the phase lock circuit PS7.

[0044]FIG. 13 is a block diagram of still another phase lock circuit PS8 according to the eighth embodiment of the present invention.

[0045]FIG. 14 is a block diagram of a phase lock circuit PS111 according to the prior art.

[0046]FIG. 15 is a time chart illustrating the operation of the phase lock circuit PS111 shown in FIG. 14.

[0047]FIG. 16 illustrates changes in the output voltage of the loop filter 2 i when the frequency (or bit rate) of the input signal 7 i (V_(IN)) is varied.

[0048]FIG. 17 is a block diagram of another phase lock circuit PS112 according to the prior art, to which a retraction circuit according to the prior art is added.

[0049]FIG. 18 is a view showing a waveform of a primary part in conventional phase synchronization circuit PS112 to which a retraction circuit was added.

[0050]FIG. 19 is a block diagram showing a phase lock circuit PS9 which is the ninth embodiment of the present invention.

[0051]FIG. 20 is a view showing waveforms of the primary parts of the phase lock circuit PS9.

[0052]FIG. 21 is a view showing the relationship between the frequency of an input signal V_(IN) 7 j and the average voltage of the phase comparator 1 j in the phase lock circuit PS9.

[0053]FIG. 22 is a view showing the relationship between the frequency of the input signal V_(IN) 7 j and the average voltage of phase comparator 1 j after the voltage tracking circuit VT9 has been stable.

[0054]FIG. 23 is a block diagram showing a phase lock circuit PS10 that is the tenth embodiment of the present invention.

[0055]FIG. 24 is a circuit diagram showing an example of Schmitt trigger circuit.

[0056]FIG. 25 is a view showing waveforms of the primary parts of the phase lock circuit PS10.

[0057]FIG. 26 is a block diagram showing a phase lock circuit PS11 that is the eleventh embodiment of the present invention.

[0058]FIG. 27 is a view showing waveforms of the primary parts of the phase lock circuit PS11 that is the eleventh embodiment of the present invention.

[0059]FIG. 28 is a block diagram showing a phase lock circuit PS12 that is the twelfth embodiment of the present invention.

[0060]FIG. 29 is a view showing waveforms of the primary parts of the phase lock circuit PS12 that is the twelfth embodiment of the present invention when it is in its locked state.

[0061]FIG. 30 is a block diagram showing a phase lock circuit PS13 that is the thirteenth embodiment of the present invention.

[0062]FIG. 31 is a view showing waveforms of the primary part of the phase lock circuit PS13.

[0063]FIG. 32 is a block diagram showing a phase lock circuit PS14 that is the fourth embodiment of the present invention.

[0064]FIG. 33 is a block diagram showing a phase lock circuit PS15 that is the fifteenth embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

[0065]FIG. 1 is a block diagram showing a phase lock circuit(phase-locked loop circuit) PS1 that is the first embodiment of the present invention in.

[0066] The phase lock circuit PS1 has a phase comparator 1 a, a loop filter 2 a, a voltage control oscillator(voltage-controlled oscillator) 3 a, a signal input terminal 7 a, a signal output terminal 9 a and a voltage tracking circuit VT1 that is an additional loop. The phase comparator 1 a, loop filter 2 a and voltage control oscillator 3 a defines the main body of a phase lock circuit. The voltage tracking circuit VT1 comprises a reference voltage generator 8 a, a differential amplifier 4 a, a filter 5 a and an adder 6 a. The phase comparator 1 a will be described to be EXOR so long as it is not particularly declined below.

[0067] The differential amplifier 4 a outputs a voltage proportional to a difference between the output voltage of the phase comparator 1 a and the output voltage V_(R) of the reference voltage generator 8 a. The filter 5 a converts the output voltage of the differential amplifier 4 a into DC voltage by integrating it. The result of integration is added to the output voltage of the phase comparator 1 a through the adder 6 a.

[0068] The voltage tracking circuit VT1 controls the average output voltage of the phase comparator 1 a so that it will coincide with the output voltage V_(R) of the reference voltage generator 8 a. In other words, the polarity in the output signal of the differential amplifier 4 a is inverted depending on the reference voltage V_(R), thereby reversing the direction of change in the output voltage of the filter 5 a (increase/decrease). More particularly, if the average output voltage of the phase comparator 1 a exceeds the reference voltage V_(R), the output signal of the differential amplifier 4 a becomes negative while if the average output voltage of phase comparator 1 a is less than the reference voltage V_(R), the output signal of the differential amplifier 4 a becomes positive. The output voltage of this differential amplifier 4 a is converted into DC voltage by integrating it at the filter 5 a. Because the output voltage of the filter 5 a is inputted into the voltage control oscillator 3 a, the average output voltage of the phase comparator 1 a is drawn to the reference voltage V_(R) whereat it is stable.

[0069] The fixation of the average voltage in the output signal of the phase comparator 1 a to the reference voltage V_(R) means that the phase difference between an input signal 7 a (V_(IN)) into the phase comparator 1 a and the output signal of the voltage control oscillator 3 a is fixed.

[0070]FIG. 2 is a view showing the dependency of the average output signal of the phase comparator 1 a on the frequency (or bit rate) of the input signal 7 a (V_(IN)) when the phase lock circuit PS1 of the first embodiment is in its locked sate (or in a state wherein the frequency in the output signal of the phase lock circuit PS1 is stable).

[0071] It is assumed in FIG. 2 that the reference voltage V_(R) generated by the reference voltage generator 8 a is a fixed voltage corresponding to the middle of the lock range.

[0072] The average voltage of the reference voltage V_(R) may exist within a range that the output voltage of the phase comparator 1 a falls. Moreover, it is not necessary that the reference voltage V_(R) is always a fixed voltage.

[0073] In Fig. (2), two straight lines shown by (i) and (ii) show characteristics for differential output voltages of the voltage tracking circuit VT1 (or differential output voltages of the filter 5 a).

[0074]FIG. 3 is a view showing signal waveforms in the primary parts of the phase lock circuit PS1 when signals having such characteristics as shown by (i) and (ii) in FIG. 2 are inputted into the phase lock circuit PS1.

[0075] It is now assumed that the phase lock circuit is in the state shown by (i) in FIG. 2 immediately after it has shifted from its unlocked state to its locked state. Since the average output signal voltage V_(R1) of the phase comparator 1 a at the present frequency of the input signal 7 a (V_(IN)) exceeds the reference voltage V_(R), the time average output signal of the differential amplifier 4 a will be offset from zero. Thus, the integrated voltage thereof occurs at the output of the filter 5 a.

[0076] In other words, when the relationship between the frequency of an input signal V_(IN) 7 i and the average output voltage of the phase comparator 1 a is as shown by (i) in FIG. 2, the frequency of the input signal is that of the input signal V_(IN) 7 i at the present time (vertical dotted line). Therefore, the average voltage V_(R1) corresponding to the intersection between two kinds of dotted lines becomes the average output voltage of the phase comparator 1 a. In the example of FIG. 2, the average voltage V_(R1) is higher than the reference voltage V_(R).

[0077] Since the average voltage V_(R1) and reference voltage V_(R) are separately determined, they will be different from each other immediately after the phase lock circuit has shifted to its locked state. The differential amplifier 4 a amplifies the difference between both the voltages and outputs an value that is zero.

[0078] If the reference voltage V_(R) can arbitrarily be determined and when the average output voltage of the phase comparator 1 a exceeds the reference voltage V_(R), this average output is determined by the phase difference between the two signals inputted into the phase comparator 1 a. Therefore, whether the average output voltage of the phase comparator 1 a is actually higher or lower than the reference voltage V_(R) is determined depending on various factors such as free-run frequency at the voltage control oscillator 3 a or the like.

[0079] On the other hand, the output voltage of the filter 5 a is applied to the voltage control oscillator 3 a as offset voltage through the adder 6 a. Because this offset voltage works to control the feed back, the output voltage of the filter 5 a approaches the characteristic shown by (ii) in FIG. 2. As the output voltage reaches the characteristic (ii), the average output voltage of the phase comparator 1 a coincides with the reference voltage V_(R). Thus, the time average output signal of the differential amplifier 4 a becomes zero and the output voltage of the filter 5 a is fixed and maintained stable.

[0080] In FIGS. 2 and 3, the duty ratio in the output voltage of the phase comparator 1 a is kept at a value near 50% since the reference voltage V_(R) is selected to be at the middle of the lock range. If the reference voltage V_(R) is selected to be lower than the middle of the lock range, the duty ratio in the output voltage of the phase comparator 1 a is kept at a value smaller than the above value. On the contrary, if the reference voltage V_(R) is selected as a voltage higher than the middle of the lock range, the duty ratio in the output voltage of the phase comparator 1 a is kept at a value higher than the above value.

[0081] In the phase lock circuit PS1, the voltage tracking circuit VT1 performs the feedback control to maintain the duty ratio of the output voltage of the phase comparator 1 a. In comparison with a phase lock circuit having no voltage tracking circuit VT1, the phase lock circuit PS1 will have its greatly enlarged lock range. By maintaining the duty ratio of the phase comparator 1 a constant, the lock range is enlarged so that the value of the duty ratio itself is not relevant to the enlargement of lock range. In other words, it is necessary for the average voltage of the reference voltage V_(R) to be within a range that the output voltage of the phase comparator 1 a can fall, but the lock range is enlarged insofar as the reference voltage V_(R) falls within that range, irrespectively of the value of the reference voltage V_(R) itself.

[0082] Although the description has been made as to the phase comparator being EXOR, the enlargement of lock range can similarly be provided even if the phase comparator is in the form of an analog mixer or set/reset flip flop. In application to CDR, the phase comparator may be of a type containing a discrimination circuit (see C. R. Hogge, JR., “A Self Correcting Clock Recovery Circuit”, Journal of Lightwave Tech., vol. LT-3, No.6, 1985, P1323 and Japanese Patent Laid-Open No. 2000-68991). Furthermore, the phase comparator may be a so-called Bang-bang type phase comparator (BB-PD) employing a delay flip flop (D-FF). When the BB-PD is used and if a drift occurs in the oscillatory frequency of voltage control oscillator, the duty ratio of the BB-PD output varies to maintain the lock even if a voltage tracking circuit is not used, although the phase relationship between the input signal and the voltage control oscillator output. At this time, the range of frequency in which the duty ratio of the BB-PD output can vary is the lock range. The addition of the voltage tracking circuit can fix the duty ratio of BB-PD output (e.g., to 50%). Thus, the lock range can broadly be enlarged. In addition, even if the phase comparator is in the form of a phase frequency comparator (PFD), the lock range can be enlarged as described.

[0083] The lock range can be enlarged when the voltage tracking circuit VT1 is applied to the phase lock circuit including the additional retraction circuit. When the phase lock circuit is shifted from its unlocked state to its locked state under action of the retraction circuit and if the duty ratio in the output voltage of the phase comparator 1 a is substantially equal to zero or even substantially equal to 100% (i.e., the retraction occurs at one end of the lock range) at this point, the voltage tracking circuit VT1 can operate to draw the duty ratio to a predetermined level and also to maintain it.

[0084] In place of the additional voltage tracking circuit, a low-pass filter or integrator having its time constant longer than that of the loop filter may be added parallel to the loop filter. This can provide a slight enlargement of lock range. However, such a method cannot arbitrarily select the output duty ratio of the phase comparator and also a sufficient advantage due to the enlargement of lock range.

[0085] The phase lock circuit of the first embodiment can provide an broader rock range and maintain the lock in any phase (which is optimum for jitter yield strength or the like) since the drift in the oscillation frequency of the voltage control oscillator is compensated by performing such a control that the average output voltage of the phase comparator coincides with any reference voltage while maintaining the average output voltage of the phase comparator at any voltage.

[0086] Since the phase lock circuit of the first embodiment can arbitrarily select any duty ratio of the phase comparator, the reference voltage can be changed depending on variation of the input data pattern or input signal level. Thus, the optimal operation for the jitter yield strength can be realized under any of various conditions.

[0087] The loop filter 2 a in the first embodiment may be a passive lag lead filter having a passive element or an active lag lead filter using an active element. Generally, the phase lock circuit employing the passive lag lead filter has its lock range narrower than that of the phase lock circuit employing the active lag lead filter. Therefore, if the voltage tracking circuit VT1 of the first embodiment is applied to the phase lock circuit employing the passive lag lead filter, the enlargement of lock range will particularly be prominently advantageous. In other words, if the aforementioned voltage tracking circuit VT1 is applied to the conventional phase lock circuit using the active lag lead filter, the phase lock circuit can use the passive lag lead filter reduced in circuit scale and simplified in design, in place of the active lag lead filter.

[0088]FIG. 4 is a block diagram showing a phase lock circuit PS2 that is the second embodiment of the present invention.

[0089] The phase lock circuit PS2 comprises a phase comparator 1 b, a loop filter 2 b, a voltage control oscillator 3 b, a signal input terminal 7 b, a signal output terminal 9 b, and a voltage tracking circuit VT2. The voltage tracking circuit VT2 comprises a reference voltage generator 8 b, a differential amplifier 4 b, a filter 5 b and an adder 6 b.

[0090] The phase lock circuit PS2 is basically the same as the phase lock circuit PS1, except that the output voltage of the filter 5 b is added to the output voltage of the loop filter 2 b rather than to the output voltage of the phase comparator 1 b.

[0091] Operation and advantage in the phase lock circuit PS2 are substantially the same as those of the phase lock circuit PS1.

[0092]FIG. 5 is a block diagram showing a phase lock circuit PS3 that is the third embodiment of the present invention.

[0093] The phase lock circuit PS3 has a phase comparator 1 c, a loop filter 2 c, a voltage control oscillator 3 c, a signal input terminal 7 c, a signal output terminal 9 c and a voltage tracking circuit VT3. The voltage tracking circuit VT3 comprises a reference voltage generator 8 c, a differential amplifier 4 c, a first filter 10 c, a second filter 5 c and an adder 6 c.

[0094]FIG. 6 is a view showing signal waveforms in the primary parts of the phase lock circuit PS3.

[0095]FIG. 6(i) is a view showing the operation of the phase lock circuit immediately after it has been shifted from its unlocked state to its locked state while FIG. 6 (ii) shows such a sate that the duty ratio in the output of the phase comparator 1 c is maintained constant (about 50% in FIG. 6) by the voltage tracking circuit VT3.

[0096] The operational principle and advantage of the phase lock circuit PS3 are substantially the same as those of the phase lock circuits PS1 and PS2 except that the phase lock circuit PS3 includes the filter 10 c inserted thereinto to provide two DC signal from the differential amplifier 4 c. Thus, the speed of computation in the differential amplifier 4 c can be reduced to lower the power consumption in comparison with the phase lock circuits PS1 and PS2.

[0097]FIG. 7 is a block diagram showing a phase lock circuit PS4 that is the fourth embodiment of the present invention.

[0098] The phase lock circuit PS4 has a phase comparator 1 d, a loop filter 2 d, a voltage control oscillator 3 d, a signal input terminal 7 d, a signal output terminal 9 d and a voltage tracking circuit VT4. The voltage tracking circuit VT4 comprises a reference voltage generator 8 d, a differential amplifier 4 d, a first filter 10 d, a second filter 5 d and an adder 6 d.

[0099] The phase lock circuit PS4 is basically the same as the phase lock circuit PS3 except that the output voltage of the filter 5 d is added to the output voltage of the loop filter 2 d rather than the output voltage of the phase comparator 1 d.

[0100] The operation and advantage of the phase lock circuit PS4 are substantially the same as those of the phase lock circuit PS3.

[0101]FIG. 8 is a block diagram showing a phase lock circuit PS5 that is the fifth embodiment of the present invention.

[0102] The phase lock circuit PS5 has a phase comparator le, a loop filter 2 e, a voltage control oscillator 3 e, a signal input terminal 7 e, a signal output terminal 9 e and a voltage tracking circuit VT5. The voltage tracking circuit VT5 comprises a reference voltage generator 8 e, a differential amplifier 4 e, a filter Se and an adder 6 e.

[0103] The phase lock circuit PS5 realizes the functions of the first filter 10 d and loop filter 2 d in the phase lock circuit PS4 through a single filter (filter 2 e). Therefore, the phase lock circuit PS5 has its reduced circuit scale smaller than that of the phase lock circuit PS4.

[0104]FIG. 9 is a block diagram showing a phase lock circuit PS6 that is the sixth embodiment of the present invention.

[0105] The phase lock circuit PS6 has a phase comparator 1 h, a loop filter 2 h, a voltage control oscillator 3 h, a signal input terminal 7 h, a signal output terminal 9 h and a voltage tracking circuit VT6. The voltage tracking circuit VT6 comprises a reference voltage generator 8 h, a differential integrator 20 and an adder 6 h.

[0106] The phase lock circuit PS6 is realized by the differential integrator 20 that is a single circuit, instead of the differential amplifier 4 a and filter 5 a in the phase lock circuit PS1. Therefore, the phase lock circuit PS6 has its reduced circuit scale smaller than those of the phase lock circuits PS1-PS5.

[0107] In each of the phase lock circuits PS2-PS5, the differential amplifier and filter may be replaced by a single differential integrator.

[0108]FIG. 10 is a circuit diagram exemplifying a configuration of the differential integrator 20.

[0109] The differential integrator 20 has an operational amplifier 13, resistors 14, 15, a capacity 16, input terminals 17, 18 and an output terminal 19. The differential integrator 20 is adapted to integrate a difference between two voltages inputted into the input terminals 17 and 18 and to output the result toward the output terminal 19 as a voltage.

[0110]FIG. 11 is a block diagram showing a phase lock circuit PS7 that is the seventh embodiment of the present invention.

[0111] The phase lock circuit PS7 has a phase comparator if, a loop filter 2 f, a voltage control oscillator 3 f, a voltage tracking circuit VT7, an adder 6 f, a signal input terminal 7 f and a signal output terminal 9 f.

[0112] The voltage tracking circuit VT7 comprises a phase comparator 11 f, a delay generator 12 f, a differential amplifier 4 f, a filter 5 f and an adder 6 f. The phase comparator 11 f and delay generator 12 f define a reference voltage generator.

[0113]FIG. 12 is a view showing waveforms of the primary parts of the phase lock circuit PS7. FIG. 12(i) is a view showing a state immediately after the phase lock circuit PS7 has been shifted from its unlocked state to its locked state while FIG. 12 (ii) shows a state in which the duty ratio in the output of the phase comparator 1 f coincides with that of the phase comparator 11 f (about 50% in FIG. 12) under action of the voltage tracking circuit VT7.

[0114]FIG. 12 shows the delay generator 12 f as one for generating a delay corresponding to 90 phase and waveforms in a case where the phase comparator 11 is formed of EXOR. Since the phase comparator 11 f receives an input signal 7 f (V_(IN)) and a signal delayed from this input signal by 90 it will output such a rectangular waveform having its duty ratio of 50% as shown in FIG. 12 (1). Thus, the average voltage in the output signal of the phase comparator 11 f coincides with the average voltage at the output signal of the phase comparator 11 f will have the duty ratio of 50%. Therefore, the phase lock circuit PS7 uses the output signal of the phase comparator 11 f as the reference voltage V_(R).

[0115] Although FIG. 12 shows both the outputs of the phase comparators 11 f and 1 f to be pulse-shaped, these output signals may be converted into DC signals by insertion of filters into the respective inputs of the differential amplifier 4 f, the DC signals being then inputted into the differential amplifier 4 f.

[0116] The phase lock circuit PS7 clearly shows the embodiment of each of the reference voltage generator in the phase lock circuits PS1-PS6 and can eliminate the adjustment of the reference voltage V_(R) by causing the phase comparator 11 f and delay generator 12 f to generate the reference voltage V_(R).

[0117]FIG. 13 is a block diagram showing a phase lock circuit PS8 that is the eighth embodiment of the present invention.

[0118] The phase lock circuit PS8 has a phase comparator 1 g, a loop filter 2 g, a voltage control oscillator 3 g, a voltage tracking circuit VT8, an adder 6 g, a signal input terminal 7 g and a signal output terminal 9 g.

[0119] The voltage tracking circuit VT8 comprises a phase comparator 11 g, a delay generator 12 g, a differential amplifier 4 g, a filter 5 g and an adder 6 g. The phase comparator 11 g and delay generator 12 g define a reference voltage generator.

[0120] The phase lock circuit PS8 generates a reference voltage in a manner different from that of the phase lock circuit PS7. Although the phase lock circuit PS7 uses the input signal 7 f (V_(IN)) as the input signal into the phase comparator 11 f and delay generator 12 f, the phase lock circuit PS8 uses the output signal of the voltage control oscillator 3 g as the input signal into the phase comparator 11 g and delay generator 12 g.

[0121] Since the phase lock circuit PS8 uses the output signal of the voltage control oscillator 3 g as the input signal into the phase comparator 11 g and delay generator 12 g, it can stably generate the reference voltage V_(R) without influence from the amplitude of the input signal 7 g (V_(IN)).

[0122] The most primary feature in the eighth embodiments is to add the voltage tracking circuit to the phase lock circuit. The voltage tracking circuit performs the control for providing an offset voltage to the voltage control oscillator such that the phase difference between the input signal and the output voltage of the voltage control oscillator (that is, to maintain the duty ratio of the phase comparator output constant).

[0123] By the way, the following embodiment provides a phase lock circuit having a signal path to which a phase comparator, loop filter, voltage control oscillator and lock detector are connected in series, the phase lock circuit further comprising voltage tracking means for adding a signal for causing the average output voltage of the phase comparator to coincide with a predetermined reference voltage to the voltage of said signal path. The lock range of the phase lock circuit is enlarged by the signal added by said voltage tracking means.

[0124]FIG. 19 is a block diagram showing a phase lock circuit PS9 that is the ninth embodiment of the present invention.

[0125] The phase lock circuit PS9 has a phase comparator 1 j, a loop filter 2 j, a voltage control oscillator 3 j, a signal input terminal 7 j, a signal output terminal 9 j, a lock detector 21 j, a retraction circuit FS2 that is an additional loop, and a voltage tracking circuit VT9 that is another additional loop.

[0126] The phase comparator 1 j, loop filter 2 j and voltage control oscillator 3 j define the main body of the phase lock circuit. The retraction circuit FS2 comprises a pulse generator 23 j, a counting circuit 24 j and a D/A converter 25 j. The voltage tracking circuit VT9 comprises a reference voltage generator 8 j, a differential integrator 20 j and an adder 6 j.

[0127]FIG. 20 is a view showing waveforms in the primary parts of the phase lock circuit PS9.

[0128]FIG. 20 (1) shows an output signal waveform of the loop filter 2 j; FIG. 20 (2) shows an output signal waveform of the lock detecting element 21 j; FIG. 20 (3) shows the average voltage in an output signal of the phase comparator 1 j; FIG. 20 (4) shows an output signal waveform of the pulse generator 23 j; and FIG. 20 (5) shows an output signal V_(FB) of the adder 22 j. FIG. 20 (3) also shows the level of the output voltage V_(R) in the reference voltage generator 8 j.

[0129] At the initial stage (left side about a dotted line) of the timing diagram, the phase lock circuit is shown in its unlocked state (or a state in which the output signal of the voltage control oscillator is asynchronous with the input signal V_(IN)). The unlocked state of the phase lock circuit is detected by the lock detector 21 j and the pulse generator 23 j generates pulses. In association with this, the counting circuit 24 j varies its count. The output voltage of the counting circuit 24 j is stepwise varied by the D/A converter 25 j. The output voltage of the D/A converter 25 j varies the oscillation frequency of the voltage control oscillator 3 j. At the time when the oscillation frequency approaches the frequency of the input signal, the phase lock circuit is retracted. Therefore, the lock detector 21 j detects the lock; the pulse generator 23 j stops; the counting circuit 24 j maintains its count constant; and the D/A converter 25 j maintains its output voltage constant. Thus, the phase lock circuit is held at its locked state (or a state in which the output signal of the voltage control oscillator is synchronous with the input signal V_(IN)). As a result, the pull-in range can be enlarged to a range in which the voltage control oscillator 3 j can vary its oscillation frequency. Such a process is the same as those of the aforementioned embodiments.

[0130] At the time when the phase lock circuit has been shifted from its unlocked state to its locked state, the output voltage V_(FB) of the adder 22 j is not necessarily at a position near the center of the lock range, but may is at a position near the lower (or upper) limit in the lock range, as shown in FIG. 20 (5). The voltage tracking circuit VT9 causes the output voltage of the adder 22 j after the lock to shift to a desired voltage (e.g., a voltage near the center of the lock range).

[0131] The operation of the voltage tracking circuit VT9 will be described in detail.

[0132]FIG. 21 is a view showing the relationship between the frequency of the input signal V_(IN) 7 j and the average voltage of the phase comparator 1 j in the phase lock circuit PS9.

[0133] In FIG. 21, (i) shows the characteristic of the phase lock circuit at the time when it has shifted from its unlocked state to its locked state. At this time, the average voltage in the output signal of the phase comparator 1 j at the frequency of the input signal V_(IN) 7 j is V_(R1) which is near the lower limit in the voltage range in which the average voltage in the output signal of the phase comparator 1 j can fall. In such a state, the locked state cannot stably be held against the environmental variation such as supply voltage variation, temperature change, jitter input or the like.

[0134] The voltage tracking circuit VT9 receives inputs V_(R) and V_(R1) and integrates a voltage proportional to the difference between these inputs, the result being then fed to the adder 22 j. As a result, the output frequency of the voltage control oscillator 3 j slightly varies to change the phase relationship between the input signal V_(IN) 7 j and the output signal of the voltage control oscillator 3 j. The average voltage in the output signal of the phase comparator 1 j approaches V_(R). As the average voltage coincides with V_(R), it will be stable (FIG. 20 (3)).

[0135] The relationship between the frequency of the input signal V_(IN) 7 j and the average voltage of the phase comparator 1 j after been stable is shown in FIG. 21 at (ii). At this time, the average voltage in the output of the phase comparator 1 j at the frequency of the input signal V_(IN) 7 j is V_(R).

[0136] When the output voltage V_(R) of the reference voltage generator 8 j is set to be near the center of the voltage range which the average voltage in the output of the phase comparator 1 j can take (FIG. 21), the output voltage V_(FB) of the adder 22 j can be moved to a point near the center of the lock range and held at that point. In such a manner, the phase lock circuit can stably be kept at its locked state against the environmental variation such as supply voltage variation, temperature change, jitter input or the like, irrespectively of the output voltage of the adder 22 j at the time when the phase lock circuit is shifted from its unlocked state to its locked state.

[0137] In the phase lock circuit PS9, moreover, the voltage tracking circuit VT9 can enlarge the lock range in addition to the enlargement of the pull-in range by the retraction circuit FS2 and the stable keeping of the locked state against the environmental variation by the voltage tracking circuit VT9.

[0138]FIG. 22 is a view showing the relationship between the frequency of the input signal V_(IN) 7 j and the average voltage of the phase comparator 1 j after the voltage tracking circuit VT9 has been stabilized.

[0139] The retraction circuit FS2 enlarges the range of the input frequency V_(IN) 7 jin in which the phase lock circuit can be shifted from its unlocked state to its locked state. Thereafter, the voltage tracking circuit V19 causes the average voltage in the output signal of the phase comparator 1 j to coincide with the output voltage V_(R) of the reference voltage generator 8 j. This coincidence can be kept to hold the locked state even if the frequency (or bit rate) of the input signal V_(IN) 7 j varies. Therefore, the lock range will be enlarged.

[0140] In comparison of the phase lock circuit PS9 with the conventional phase lock circuit PS112, the central part of FIG. 22, that is, the frequency range of the input signal V_(IN) 7 j in which the average voltage in the output signal of the phase comparator 1 j coincides with the output voltage V_(R) of the reference voltage generator 8 j is an increase on the lock range by addition of the voltage tracking circuit VT9. This increase on the lock range can arbitrarily be selected by varying the output voltage ranges of the retraction circuit FS2 and voltage tracking circuit V19, independently of the characteristic of the loop filter 2 j. In other words, the lock range can be enlarged without deterioration of the phase noise and jitter yield strength in the output of the phase lock circuit.

[0141] If it is simply wanted to enlarge the lock range, the output voltage V_(R) of the reference voltage generator 8 j may be set in the voltage range that the average voltage in the output of the phase comparator 1 j can be taken. Thus, the lock range can be enlarged irrespectively of its set value. Furthermore, if the output voltage V_(R) of the reference voltage generator 8 j is set at a point near the center of the voltage range that the average voltage in the output signal of the phase comparator 1 j can be taken, the locked state can more stably be maintained against the environmental variation such as supply voltage variation, temperature change, jitter input or the like.

[0142]FIG. 23 is a block diagram showing a phase lock circuit PS10 that is the tenth embodiment of the present invention.

[0143] The phase lock circuit PS10 has a phase comparator 1 k, a loop filter 2 k, a voltage control oscillator 3 k, a signal input terminal 7 k, a signal output terminal 9 k, a lock detector 21 k, a retraction circuit FS3 that is an additional loop, and a voltage tracking circuit VT10 that is another additional loop.

[0144] The phase comparator 1 k, loop filter 2 k and voltage control oscillator 3 k define the main body of the phase lock circuit. The retraction circuit FS3 comprises a Schmitt trigger circuit 26 k, an integrator 27 and a voltage holding circuit 28. The voltage tracking circuit VT10 comprises a reference voltage generator 8 k, a differential integrator 20 k and an adder 6 k. The additional retraction circuit in the conventional phase lock circuit PS112 is generally of a digital circuit for such a purpose that the variation in the output voltage of the retraction circuit FS1 can be suppressed to maintain the locked state stable. However, if the voltage tracking circuit is applied with the retraction circuit, the voltage tracking circuit can cancel any variation occurring in the output of the retraction circuit to greatly reduce the requirement of performance in the retraction circuit. Thus, the retraction circuit can be formed by an analog circuit reduced in circuit scale and power consumption. This can be accomplished by the retraction circuit FS3 according to the tenth embodiment of the present invention.

[0145]FIG. 24 is a circuit diagram showing an example of the Schmitt trigger circuit.

[0146] The Schmitt trigger circuit 26 k may be a circuit which has hysteresis characteristics in the input and output (a history circuit), such as a Schmitt trigger inverter shown in FIG. 24 (1) or a hysteresis comparator shown in FIG. 24 (2) and (3). Since the Schmitt trigger type digital gate and analog hysteresis comparator are identical in electrical function with each other and only different from each other relating to the voltage used and term depending on the application, the tenth embodiment can use either of these circuits. In this description, these circuits will be referred to as Schmitt trigger circuit as the general term of such a circuitry as having hysteresis characteristics in input and output.

[0147] The Schmitt trigger circuit 26 k and integrator 27 define an analog oscillator. The voltage holding circuit 28 causes the analog oscillator to output a signal when the lock detector 21 k judges the unlocked state and holds and outputs a constant voltage when the lock detector 21 k judges the locked state.

[0148]FIG. 25 is a view showing waveforms in the primary parts of the phase lock circuit PS10.

[0149]FIG. 25 (1) shows the output of the loop filter 2 k; FIG. 25 (2) shows the output signal of the lock detector 21 k; FIG. 25 (3) shows the output signal of the voltage holding circuit 28; and FIG. 25 (4) shows the output voltage V_(FB) of the adder 22 k.

[0150] At the initial stage (left side about a dotted line) of timing diagram, the phase lock circuit is in its unlocked state which is detected by the lock detector 21 k to cause the analog oscillator formed by the Schmitt trigger circuit 26 k and integrator 27 to generate a triangular wave. The triangular wave sweeps the output frequency of the voltage control oscillator 3 k. At the time when the output frequency approaches the frequency of the input signal, the phase lock circuit is retracted. Thereafter, the lock detector 21 n detects the locked state. The output voltage of the lock detector 21 n is maintained constant to hold the locked state of the phase lock circuit by the voltage holding circuit 28. As a result, the pull-in range can be enlarged to a range in which the voltage control oscillator 3 k can vary its oscillation frequency.

[0151] On the other hand, after the phase lock circuit has shifted from its unlocked state to its locked state, the output voltage V_(FB) of the adder 22 k is drawn to the desired voltage (e.g., a point near the center of the lock range) and stably held at the level by the voltage tracking circuit VT10. In other words, the lock range is enlarged by the voltage tracking circuit VT10.

[0152] The phase lock circuit PS 10 is characterized by that it is reduced in circuit scale and power consumption, in addition to the enlargement of the pull-in and lock ranges and the resistance against the environmental variation such as supply voltage variation, temperature change, jitter input or the like, in comparison with the phase lock circuit PS9.

[0153]FIG. 26 is a block diagram showing a phase lock circuit PS11 that is the eleventh embodiment of the present invention.

[0154] The phase lock circuit PS11 has a phase comparator 1 m, a loop filter 2 m, a voltage control oscillator 3 m, a signal input terminal 7 m, a signal output terminal 9 m, a lock detector 21 m, a retraction circuit FS 4 that is an additional loop and a voltage tracking circuit VT11 that is another additional loop.

[0155] The phase comparator 1 m, loop filter 2 m and voltage control oscillator 3 m define the main body of the phase lock circuit. The retraction circuit FS4 comprises a Schmitt trigger circuit 26 m, a differential integrator 20 m and a switch 29. The voltage tracking circuit VT11 comprises a reference voltage generator 8 m, a differential integrator 20 m and an adder 6 m. The retraction circuit FS4 and voltage tracking circuit VT11 share the differential integrator 20 m to form a common circuit CM1.

[0156]FIG. 27 is a view showing waveforms in the primary parts of the phase lock circuit PS11 that is the eleventh embodiment of the present invention.

[0157]FIG. 27 (1) shows the output signal of the loop filter 2 m; FIG. 27 (2) shows the output signal of the lock detector 21 m; FIG. 27 (3) shows the average voltage in the output signal of the phase comparator 1 m; and FIG. 27 (4) shows the output voltage V_(FB) of the differential integrator 20 m. FIG. 27 (3) also shows the output voltage V_(R) of the reference voltage generator 8 m.

[0158] At the initial stage (left side about a dotted line) of the timing diagram, the phase lock circuit is in its unlocked state; the lock detector 21 m judges the unlocked state; the switch 29 selects the output signal of the Schmitt trigger circuit 26 m; and an analog oscillator formed by the Schmitt trigger circuit 26 m and differential integrator 20 m generates a triangular wave. The triangular wave sweeps the output frequency of the voltage control oscillator 3 m. At the time when the output frequency approaches the frequency of the input signal, the phase lock circuit is retracted. Thereafter, the lock detector 21 m determines the lock. The switch 29 selects the output signal of the phase comparator 1 m. The voltage tracking circuit VT11 controls the average voltage in the output of the phase comparator 1 m (FIG. 27 (3)) so that it will coincide with the output voltage V_(R) of the reference voltage generator. Thus, the lock state will be held stably. As a result, the pull-in range can be enlarged to the range in which the voltage control oscillator 3 k can vary its oscillation frequency. Even though a jump occurs in the voltage inputted into the differential integrator 20 m on switching of the switch 29, no jump will appear in the output of the differential integrator 20 m. Therefore, the phase lock circuit can smoothly be shifted from its unlocked state to its locked state.

[0159] The Schmitt trigger circuit 26 m may be any of various forms insofar as having hysteresis characteristics in input and output, such as a Schmitt trigger type digital gate or a hysteresis comparator. The switch 29 may be any analog switch. Since the phase comparator 1 m and Schmitt circuit 26 m can use digital type switches, however, the switch 29 may be realized by use of a digital gate type selector.

[0160] The output waveform of the analog oscillator is not limited to triangular waveform, but may be in the form of saw-tooth wave by differing the time constant in the voltage increasing process from that in the voltage decreasing process.

[0161] Although FIG. 26 has been described in connection with such a configuration that the output voltage V_(R) of the reference voltage generator 8 m is inputted into one of the inputs in the differential integrator 20 m, irrespectively of the state of the switch 29, such a configuration is out of the period in which the switch 29 selects the Schmitt trigger 26 m. In other words, when the switch 29 selects the Schmitt trigger 26 m, one of the inputs of the differential integrator 20 m (which receives the output voltage V_(R) of the reference voltage generator 8 m in FIG. 26) may provide any voltage within a range between the maximum and minimum voltages in the Schmitt trigger 26 m, rather than the output voltage V_(R) of the reference voltage generator 8 m.

[0162] The phase lock circuit PS11 is further advantageous in that the retraction circuit FS4 and voltage tracking circuit VT11 share the common circuit CM1 to reduce both the circuit scale and power consumption, in addition to the enlargement of the pull-in and lock ranges and the resistance against the environmental variation such as supply voltage variation, temperature change, jitter input or the like, as in the phase lock circuits PS9 and PS10.

[0163] In the common circuit CM1, the retraction circuit FS 4 operates in the unlocked state while the voltage tracking circuit VT11 operates in the locked state. Since both the circuits will not simultaneously operate, it is advantageous in that there will not occur the reduction of operational speed due to the reverse control, the reduction of the effectively controllable range and so on.

[0164] Moreover, the phase lock circuit can smoothly be shifted from its unlocked state to its locked state since no jump will occur in the output voltage of the differential integrator 20 m which is fed back to the main body of the phase lock circuit. This is advantageous in that the unlocked state hardly occurs due to any impact of shifting.

[0165]FIG. 28 is a block diagram showing a phase lock circuit PS12 that is the twelfth embodiment of the present invention.

[0166] The phase lock circuit PS1 has a phase comparator 1 p, a loop filter 2 p, a voltage control oscillator 3 p, a signal input terminal 7 p, a signal output terminal 9 p and a voltage tracking circuit VT1 that is an additional loop.

[0167] The phase comparator 1 p, loop filter 2 p and voltage control oscillator 3 p define the main body of the phase lock circuit. The voltage tracking circuit VT12 comprises a reference voltage generator 8 p, a voltage difference detector 40 p, a comparator 41 p, a pulse generator 23 p, a counting circuit 24 p and a D/A converter 25 p.

[0168] The voltage tracking circuit VT11 of the phase lock circuit PS12 is of a digital type corresponding to the voltage tracking circuit VT1 of the phase lock circuit PS1. The operational principle thereof is substantially the same as that of the phase lock circuit PS1. The voltage difference detector 40 p receives the output of the phase comparator 1 p and the output voltage V_(R) of the reference voltage generator 8 p. If the difference between these voltages (or the difference between the averages for both the voltages) exceeds a predetermined voltage, the voltage difference detector 40 p feeds an enable signal EN to the pulse generator 23 p which is in turn oscillated.

[0169] On the other hand, the comparator 41 p receives the output of the phase comparator 1 p and the output voltage V_(R) of the reference voltage generator 8 p and compares them relating to the voltage (or the average voltage) to generate an output U/D signal which is in turn outputted therefrom toward the counting circuit 24 p. The output signal of the pulse generator 23 p is inputted into and counted by the counting circuit 24 p. At this time, the direction of counting (up/down) is determined by the output U/D signal of the comparator 41 p. The output of the counting circuit 24 p is converted into a voltage by the D/A converter 25 p, this voltage being added to the voltage path in the main body of the phase lock circuit. In such an arrangement, the voltage tracking circuit VT12 controls the average voltage in the output of the phase comparator 1 p so that it will coincide with the output voltage V_(R) of the reference voltage generator 8 p.

[0170]FIG. 29 is a view showing waveforms in the primary parts of the phase lock circuit PS12 that is the twelfth embodiment of the present invention when it is in its locked state.

[0171]FIG. 29 (1) shows the output signal EN of the voltage difference detector 40 p; FIG. 29 (2) shows the output signal of the pulse generator 23 p; FIG. 29 (3) shows the output voltage V_(FB) of the D/A converter 25 pp; and FIG. 29 (4) shows the average voltage in the output signal of the phase comparator 1 p. FIG. 29 (4) also shows the output voltage V_(R) of the reference voltage generator 8 p.

[0172] If the average voltage in the output of the phase comparator 1 p is shifted to exceed the detection threshold (FIG. 29 (4)) of the voltage difference detector 40 p due to the environmental variation such as supply voltage variation, temperature change or the like or the aged deterioration, the voltage difference detector 40 p outputs the enable signal EN toward the pulse generator 23 p which is in turn oscillated.

[0173] The counting circuit 24 p varies its count in the direction (up/down) specified by the comparator 41 p. Thus, the D/A converter 25 p varies its output voltage V_(FB). In association with this, the phase relationship between the average voltage in the output of the phase comparator 1 p and the input signal 7 pV_(IN) varies to approach the average voltage in the output of the phase comparator 1 p to the output voltage V_(R) of the reference voltage generator 8 q. If the average voltage in the output of the phase comparator 1 p as well as the output voltage V_(R) of the reference voltage generator 8 q decreases to be lower than the aforementioned threshold, the voltage difference detector 40 p inverts the enable output EN to stop the pulse generator 23 p. As a result, the average voltage in the output of the phase comparator 1 p is held at a point near the output voltage V_(R) of the reference voltage generator 8 q. Thus, the locked state can be maintained stable.

[0174] Even though the frequency (or bit rate) of the input signal 7 pV_(IN) varies, the voltage tracking circuit VT12 can held the average voltage in the output of the phase comparator 1 p at a level near the output voltage V_(R) of the reference voltage generator 8 q. Namely, the voltage tracking circuit VT12 can enlarge the lock range.

[0175] The voltage difference detector 40 p is interposed in order to provide a dead band in the operation of the voltage tracking circuit VT12. In other words, if the output voltage (or average voltage) of phase comparator 1 p and the output voltage V_(R) of the reference voltage generator 8 p are within a predetermined voltage difference, the pulse generator 23 p and voltage tracking circuit VT12 are turned off. This minimizes the influence of the voltage tracking circuit VT12 on the operation of the main phase lock circuit body. If the influence of the voltage tracking circuit VT12 on the main phase lock circuit body raises no problem, the voltage difference detector 40 p may be omitted and the pulse generator 23 p may always be oscillated.

[0176] Although the phase lock circuit PS12 has been described as to its configuration that the output voltage of the phase comparator 1 p is inputted into the voltage tracking circuit VT12, the output of which is added to the output of the phase comparator 1 p, the output signal of the voltage tracking circuit VT12 may be added to the output signal of the loop filter 2 p. Alternatively, the output signal of the loop filter 2 p may be inputted into the voltage tracking circuit VT12, the output signal of which is added to the output signal of the loop filter 2 p. In addition, the voltage difference detector 40 p may be either of the hysteresis comparator or window comparator.

[0177] When the voltage tracking circuit VT12 is added to the phase lock circuit PS12, the lock range is enlarged. The digital form of the voltage tracking circuit VT12 is advantageous in that it can easily be integrated and hardly be influenced by the environmental variation such as supply voltage variation, temperature change or the like. Since the voltage difference detector 40 p provides a dead band in the operation of the voltage tracking circuit VT12, the influence of the voltage tracking circuit VT12 on the operation of the main phase lock circuit body can advantageously be minimized.

[0178]FIG. 30 is a block diagram showing a phase lock circuit PS13 that is the thirteenth embodiment of the present invention.

[0179] The phase lock circuit PS13 has a phase comparator 1 q, a loop filter 2 q, a voltage control oscillator 3 q, a signal input terminal 7 q, a signal output terminal 9 q, a lock detector 21 q, a retraction circuit FS5 that is an additional loop and a voltage tracking circuit VT13 that is another additional loop.

[0180] The phase comparator 1 q, loop filter 2 q and voltage control oscillator 3 q define the main body of the phase lock circuit. The retraction circuit FS5 comprises a pulse generator 23 q, a counting circuit 24 q, and a D/A converter 25 q. The voltage tracking circuit VT13 comprises a reference voltage generator 8 q, a voltage difference detector 40 q, a comparator 41 q, a pulse generator 23 q, a counting circuit 24 q and a D/A converter 25 q. The retraction circuit FS5 and voltage tracking circuit VT13 share part of the circuitry (including the pulse generator 23 q, counting circuit 24 q and D/A converter 25 q) to form a common circuit CM2.

[0181] In the phase lock circuit PS13, the voltage tracking circuit VT12 of the phase lock circuit PS12 is applied to the conventional phase lock circuit PS112 having the additional retraction circuit (FIG. 17). The retraction circuit and voltage tracking circuit share the pulse generator, counting circuit and D/A converter to form the common circuit CM2.

[0182] The operation of the retraction circuit FS5 is the same as that of the phase lock circuit PS9 while the operation of the voltage tracking circuit VT13 is the same as that of the phase lock circuit PS12.

[0183]FIG. 31 is a view showing waveforms in the primary parts of the phase lock circuit PS13.

[0184]FIG. 31 (1) shows the output signal of the loop filter 2 q; FIG. 31 (2) shows the output signal of the lock detector 21 q; FIG. 31 (3) shows the output signal EN of the voltage difference detector 40 q; FIG. 31 (4) shows the output signal of the pulse generator 23 q; FIG. 31 (5) shows the output signal of the D/A converter 25 q; and FIG. 31 (6) shows the average voltage in the output signal of the phase comparator 1P. FIG. 31 (6) also shows the detection threshold of the voltage difference detector 40 q.

[0185] At the initial stage (left side about a dotted line, left side) of the timing diagram, the phase lock circuit is in its unlocked state; the lock detector 21 q discriminates the unlocked state; and the pulse generator 23 q generates pulses. Thus, the D/A converter 25 q varies the voltage stepwise.

[0186] When the phase lock circuit PS13 is brought into its locked state, the lock detector 21 q judges the locked state. At this time point, the average voltage in the output of the phase comparator 1 q does not coincide with the output voltage V_(R) of the reference voltage generator 8 q. The voltage difference detector 40 q outputs an enable signal EN. Thus, the pulse generator 23 q continues to oscillate. When the output voltage V_(FB) of the D/A converter 25 q varies, the phase relationship between the output signal of voltage control oscillator 3 q and the input signal 7 qV_(IN) also varies. Thus, the average voltage in the output of the phase comparator 1 q also varies.

[0187] As the average voltage in the output of the phase comparator 1 q coincides with the output voltage V_(R) of the reference voltage generator 8 q (strictly spealing, it falls within the threshold shown in FIG. 3 (6)), it is detected by the voltage difference detector 40 q to stop the pulse generator 23 q, thereby maintaining the locked state. Subsequently, even though the environmental variation such as supply voltage variation, temperature change or the like occurs to shift the average voltage in the output of the phase comparator 1 q, such a shift is detected by the voltage difference detector 40 q to oscillate the pulse generator 23 q. The counting circuit 24 q varies its count in the direction that cancels the aforementioned voltage shift. Thus, the phase lock circuit can be returned to its original state without unlocking. As a result, the locked state thereof can be maintained.

[0188] The phase lock circuit PS13 is advantageous in that the retraction circuit FS5 and voltage tracking circuit VT13 share the common circuit CM2 to reduce both the circuit scale and power consumption, in addition to the enlargement of the pull-in and lock ranges and the resistance against the environmental variation such as supply voltage variation, temperature change, jitter input or the like, as in the phase lock circuits PS11.

[0189] Since the phase lock circuit PS13 does not generate a jump on the output voltage of D/A converter 25 q which is fed back to the main phase lock circuit body, it can smoothly be shifted from its unlocked state to its locked state, thereby hardly unlocking the phase lock circuit due to the impact of shift. The phase lock circuit PS13 compares the digital circuit performing the same function as that of the phase lock circuit PS11. Therefore, the phase lock circuit PS13 is more advantageous in the it can easily be integrated and hardly influenced by the environmental variation such as supply voltage variation, temperature change or the like.

[0190] In other words, each of the aforementioned embodiments provides a phase lock circuit comprising a signal path to which a phase comparator, a loop filter and a voltage control oscillator are connected in series, said phase comparator being adapted to compare the phase of an input signal V with the phase in the output signal of said voltage control oscillator and to output its result of comparison, said loop filter being adapted to receive the output signal of said phase comparator and to output a DC voltage; said voltage control oscillator being adapted to control the output oscillation frequency depending on the DC output voltage of said loop filter, said phase lock circuit further comprising voltage tracking means for adding, to the voltage of said signal path, a signal causing the average voltage in the output voltage of said phase comparator to coincide with a predetermined reference voltage, whereby said voltage tracking means can enlarge the lock range in said phase lock circuit.

[0191] Therefore, according to the aforementioned embodiments, the problem of the prior art in that the limitation of the duty ratio in the output of the phase comparator directly restricts the lock range can be overcome. Thus, the lock range can greatly be enlarged to the range of input frequency in which the voltage tracking circuit can maintain the duty ratio of the phase comparator output constant.

[0192] By adding the additional loop (or voltage tracking circuit) to the conventional phase lock circuit, the aforementioned embodiments can hold the synchronous state and extremely enlarge the lock range in comparison with the conventional phase lock circuit, without change of the duty ratio in the phase comparator output, even though the input frequency (or bit rate) varies or the voltage control oscillator is agedly deteriorated or the temperature varies.

[0193] The aforementioned embodiments are further advantageous in that the phase relationship between the input signal V_(IN) and the output of the voltage control oscillator can arbitrarily be controlled by regulating the reference voltage V_(R) of the voltage tracking circuit. With application to CDR, the aforementioned embodiments are further advantageous in that the yield strength against the jitter can always be maintained higher since the most allowable phase relationship can always be used.

[0194] This advantage can be provided similarly to a phase lock circuit which has its substantial lock range reduced by adding a retraction circuit thereto. In other words, even though the phase lock circuit having the additional retraction circuit is retracted at the end of the lock range, the lock range can greatly be enlarged since the voltage tracking circuit draws and holds the phase lock circuit to a predetermined duty ratio. Namely, the aforementioned embodiments can eliminate any additional circuit for compensating the aged variation and temperature change and greatly reduce the operation required by the regulation and the manufacturing cost.

[0195]FIG. 32 is a block diagram showing a phase lock circuit PS14 that is the fourth embodiment of the present invention.

[0196] The phase lock circuit PS14 has a phase comparator 1 r, a loop filter 2 r, a voltage control oscillator 3 r, a voltage tracking circuit VT14, a signal input terminal 7 r and a signal output terminal 9 r.

[0197] The voltage tracking circuit VT14 comprises a phase comparator 11 r, a variable delay generator 12 r, a differential amplifier 4 r, a filter 5 r, an adder 6 r and an oscillator 41. The phase comparator 11 r, variable delay generator 12 r and oscillator 41define a reference voltage generator.

[0198] The phase lock circuit PS14 generates a reference voltage in a manner different from that of the phase lock circuit PS7. In other words, the delay generator 12 f of the phase lock circuit PS7 generates a fixed delay (e.g., a delay corresponding to 90 degrees phase) while the phase lock circuit PS14 uses the variable delay generator 12 r (e.g., an infinite phase shifter for generating delays corresponding to 0-360 degrees phase). Furthermore, the quantity of delay in the variable delay generator 12 r is periodically controlled by the oscillator 41.

[0199] In the phase lock circuit PS7, the reference voltage generator formed by the phase comparator 11 f and delay generator 12 f outputs a rectangular wave having its duty ratio of 50% as shown FIG. 12 (1) and (2). On the contrary, in the phase lock circuit PS14, the reference voltage generator formed by the phase comparator 11 r, variable delay generator 12 r and oscillator 41 outputs a rectangular wave having its duty ratio which is randomly variable between 0 and 100%. The variable duty ratio is provided from the fact that the oscillation frequency of the oscillator 41 is determined independently of the frequency (or bit rate) of the input signal 7 r, thereby always varying the phase relationship.

[0200] In such a manner, the output of the reference voltage generator in the phase lock circuit PS14 has its duty ratio which is a randomly variable rectangular wave. High and low appear substantially at the same probability. Therefore, the output of the reference voltage generator will contain DC components substantially equal to those in the case where the duty ratio is fixed at 50% (as in the phase lock circuit PS7). Therefore, the reference voltage generator in the phase lock circuit PS14 can generate the reference voltage V_(R) of the voltage tracking circuit VT14.

[0201] Although in the arrangement of the phase lock circuit PS14 shown in FIG. 32, both the output signals of the phase comparator 11 r and phase comparator 1 r are in the form of pulse signal, only DC components may be extracted by inserting filters into the respective inputs of the differential amplifier 4 r, these DC signals being then inputted into the differential amplifier 4 r. In this case, the similar operation can be realized even though high-frequency components have previously be removed as described, since the high-frequency components are finally removed by the filter 5 r in the voltage tracking circuit VT14.

[0202] The reference voltage generator in the phase lock circuit PS14 does not have to adjust the delay in the delay generator (e.g., it adjusts into a fixed delay corresponding to 90 degrees phase). This is advantageous in that the yield strength is stronger against the aged deterioration and environmental variation such as supply voltage variation, temperature change or the like.

[0203] In other words, in the phase lock circuit PS14, the variable delay generator 12 r in the reference voltage generator is an example of variable delay means for delaying the input signal V_(IN) for any time period. The oscillator 41 is an example of oscillation means for oscillating a signal having a predetermined frequency for periodically controlling the delay in said variable delay means. The phase comparator 11 r is an example of the second phase comparator which compares the phase of the input signal V_(IN) with the output phase of said variable delay means.

[0204]FIG. 33 is a block diagram showing a phase lock circuit PS15 that is the fifth embodiment of the present invention.

[0205] The phase lock circuit PS15 has a phase comparator 1 s, a loop filter 2 s, a voltage control oscillator 3 s, a voltage tracking circuit VT15, a signal input terminal 7 s and a signal output terminal 9 s.

[0206] The voltage tracking circuit VT15 comprises a phase comparator 11 s, a differential amplifier 4 s, a filter 5 s, an adder 6 s and an oscillator 42. The phase comparator 11 s and oscillator 42 define a reference voltage generator.

[0207] The phase lock circuit PS15 generates a reference voltage in a manner different from that of the phase lock circuit PS14. The phase lock circuit PS14 uses the variable delay generator 12 r while the phase lock circuit PS15 does not use any delay generator and is adapted to input the output of the oscillator 42 directly into the phase comparator 11 s. Since the oscillation frequency of the oscillator 42 is determined independently of the frequency (or bit rate) of the input signal 7 s, the phase comparator 11 s will output a rectangular wave having its duty ratio which is randomly variable between 0 and 100%. Since the output of the reference voltage generator in the phase lock circuit PS15 is a rectangular wave having its randomly variable duty ratio, high and low appear substantially at the same probability. Thus, The output will contain DC components substantially equal to those of the case where the duty ratio is fixed at 50% (or phase lock circuit PS7). Therefore, the reference voltage generator of the phase lock circuit PS15 can generate the reference voltage of the voltage tracking circuit VT15.

[0208] In the configuration of the phase lock circuit PS15 shown in FIG. 33, both the output signals of the phase comparator 11 s and phase comparator is are in the form of pulse signal. However, only DC components may be extracted by inserting filters into the respective inputs of the differential amplifier 4 s, these DC signals being then inputted into the differential amplifier 4 s.

[0209] The reference voltage generator in the phase lock circuit PS15 ideally covers the duty ratio in the output of the phase comparator 11 s between 0 and 100%, in addition to provision of a simplified and size-reduced circuitry, in comparison with the reference voltage generator of the phase lock circuit PS14. The probability in which high and low appear can be approached to about 50% with improved accuracy. Therefore, the reference voltage of the voltage tracking circuit VT15 can be generated in a more stable manner.

[0210] In the phase lock circuit PS15, the oscillator 42 is an example of oscillation means for oscillating a signal having a predetermined frequency. The phase comparator 11 s is an example of the second phase comparator which compares the phase of the above-mentioned input signal V_(IN) with that of the output signal from said oscillation means. 

1. A phase lock circuit(phase-locked loop circuit) having a signal path to which a phase comparator, a loop filter and a voltage control oscillator(voltage-controlled oscillator) are connected in series, said phase comparator being adapted to compare the phase of an input signal V_(IN) with the phase in the output signal of said voltage control oscillator and to output its result of comparison, said loop filter being adapted to receive the output signal of said phase comparator and to output a DC voltage; said voltage control oscillator being adapted to control the output oscillation frequency depending on the DC output voltage of said loop filter, said phase lock circuit further comprising voltage tracking means for adding, to the voltage of said signal path, a signal causing the average voltage in the output voltage of said phase comparator to coincide with a predetermined reference voltage, whereby said voltage tracking means can enlarge the lock range in said phase lock circuit.
 2. A phase lock circuit(phase-locked loop circuit) having a signal path to which a phase comparator, a loop filter, a voltage control oscillator(voltage-controlled oscillator), a lock detector and a retraction circuit are connected, said phase comparator being adapted to compare the phase of an input signal V_(IN) with the phase in the output signal of said voltage control oscillator and to output its result of comparison, said loop filter being adapted to receive the output signal of said phase comparator and to output a DC voltage; said voltage control oscillator being adapted to control the output oscillation frequency depending on the DC output voltage of said loop filter, said lock detector being adapted to judge whether the output signal of the said voltage control oscillator is locked or unlocked relative to said input signal V_(IN) and to output the judgment result, said retraction circuit being a signal generator which is adapted to a scanning signal if said lock detector judges the unlocked state and to add the scanning signal to the voltage of said signal path, said phase lock circuit further comprising voltage tracking means for adding, to the voltage of said signal path, a signal causing the average voltage in the output voltage of said phase comparator to coincide with a predetermined reference voltage, whereby said voltage tracking means can enlarge the lock range in said phase lock circuit.
 3. The phase lock circuit according to claim 1 wherein said voltage tracking means comprises reference voltage generator means for generating a voltage within the output voltage range of said phase comparator, a differential amplifier for outputting a voltage proportional to a difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means, a filter for converting the output of said differential amplifier into DC voltage, and adder means for adding the output of said filter to the output voltage of said phase comparator and for delivering the result to said loop filter.
 4. The phase lock circuit according to claim 2 wherein said voltage tracking means comprises reference voltage generator means for generating a voltage within the output voltage range of said phase comparator, a differential amplifier for outputting a voltage proportional to a difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means, a filter for converting the output of said differential amplifier into DC voltage, and adder means for adding the output of said filter to the output voltage of said phase comparator and for delivering the result to said loop filter.
 5. The phase lock circuit according to claim 1 wherein said voltage tracking means comprises reference voltage generator means for generating a voltage within the output voltage range of said phase comparator, a differential amplifier for outputting a voltage proportional to a difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means, and adder means for adding the output of said filter to the output voltage of said phase comparator and for delivering the result to said loop filter.
 6. The phase lock circuit according to claim 2 wherein said voltage tracking means comprises reference voltage generator means for generating a voltage within the output voltage range of said phase comparator, a differential amplifier for outputting a voltage proportional to a difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means, and adder means for adding the output of said filter to the output voltage of said phase comparator and for delivering the result to said loop filter.
 7. The phase lock circuit according to claim 3 or 5 wherein the DC voltage converted from the output voltage of said phase comparator by said filter is inputted into said voltage tracking means.
 8. The phase lock circuit according to claim 4 or 6 wherein the DC voltage converted from the output voltage of said phase comparator by said filter is inputted into said voltage tracking means.
 9. The phase lock circuit according to any one of claims 3, 5 and 7 wherein said reference voltage generator means comprises delay means for delaying said input signal V_(IN) for a predetermined time period, and a second phase comparator for receiving said input signal V_(IN) and the output of said delay means.
 10. The phase lock circuit according to any one of claims 4, 6 and 8 wherein said reference voltage generator means comprises delay means for delaying said input signal V_(IN) for a predetermined time period, and a second phase comparator for receiving said input signal V_(IN) and the output of said delay means.
 11. The phase lock circuit according to any one of claims 3, 5 and 7 wherein said reference voltage generator means comprises delay means for delaying the output signal of said voltage control oscillator for a predetermined time period and a second phase comparator for receiving the output signal of said voltage control oscillator and the output signal of said delay means.
 12. The phase lock circuit according to any one of claims 4, 6 and 8 wherein said reference voltage generator means comprises delay means for delaying the output signal of said voltage control oscillator for a predetermined time period and a second phase comparator for receiving the output signal of said voltage control oscillator and the output signal of said delay means.
 13. The phase lock circuit according to any one of claims 3, 5, 7, 9 and 11 wherein said addition is carried out relative to the DC output voltage of said loop filter in said signal path.
 14. The phase lock circuit according to any one of claims 4, 6, 8, 10 and 12 wherein said addition is carried out relative to the DC output voltage of said loop filter in said signal path.
 15. The phase lock circuit according to claim 1 wherein said voltage tracking means comprises reference voltage generator means for generating a voltage within the output voltage range of said phase comparator, voltage difference detector means for detecting a potential difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means when it exceeds a predetermined value, voltage comparator means for detecting a voltage difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means, pulse generator means for performing an oscillation when the voltage difference detector means detects that the potential difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means exceeds said predetermined value, counter means for counting the output of said pulse generator means, the direction of counting being controlled by the output of said voltage comparison means, and D/A converter means for converting the result of count from said counter means into a voltage.
 16. The phase lock circuit according to claim 2 wherein said voltage tracking means comprises reference voltage generator means for generating a voltage within the output voltage range of said phase comparator, voltage difference detector means for detecting a potential difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means when it exceeds a predetermined value, voltage comparator means for detecting a voltage difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means, pulse generator means for performing an oscillation when the voltage difference detector means detects that the potential difference between the output voltage of said phase comparator and the output voltage of said reference voltage generator means exceeds said predetermined value, counter means for counting the output of said pulse generator means, the direction of counting being controlled by the output of said voltage comparison means, and D/A converter means for converting the result of count from said counter means into a voltage.
 17. The phase lock circuit according to any one of claims 2, 4, 6, 8, 10, 12, 14 and 16 wherein said retraction means comprises pulse generator means for continuing pulses with a predetermined cycle when said lock detector means detects the unlock, counter means for counting the number of pulses from said pulse generator means, and D/A converter means for converting the result of count from said counter means into a voltage.
 18. The phase lock circuit according to any one of claims 2, 4, 6, 8, 10, 12, 14 and 16 wherein said retraction means comprises Schmitt trigger means, integration means for integrating the output voltage of said Schmitt trigger means and for feeding the result of integration back to the input of said Schmitt trigger means, and voltage holding means for outputting the output voltage of said integration means when said lock detector means judges the unlock and for outputting a constant voltage when said lock detector means judges the lock.
 19. The phase lock circuit according to any one of claims 2, 4, 6, 8, 10, 12, 14 and 16 wherein said retraction means Schmitt trigger means for receiving the output voltage of said voltage tracking means, and circuit switching means for feeding the output of said Schmitt trigger means to said voltage tracking means when said lock detector means detects the unlock and for feeding the output of said phase comparator to the input of said voltage tracking means when said lock detector means detects the lock.
 20. The phase lock circuit according to any one of claims 2, 4, 6, 8, 10, 12, 14 and 16 wherein said retraction means wherein at least one of the pulse generator means, counter means and D/A converter means included in said retraction means and the pulse generator means, counter means and D/A converter means included in said voltage tracking means is shared by said retraction means and voltage tracking means.
 21. The phase lock circuit according to any one of claims 3, 5 and 7 wherein said reference voltage generator means comprises variably delay means for delaying said input signal V_(IN) for any time period, oscillation means for oscillating a signal having a predetermined frequency to periodically control the delay in said variable delay means, and a second phase comparator for comparing the phase of said input signal V_(IN) with the phase in the output signal of said variable delay means.
 22. The phase lock circuit according to any one of claims 4, 6 and 8 wherein said reference voltage generator means comprises variably delay means for delaying said input signal V_(IN) for any time period, oscillation means for oscillating a signal having a predetermined frequency to periodically control the delay in said variable delay means, and a second phase comparator for comparing the phase of said input signal V_(IN) with the phase in the output signal of said variable delay means.
 23. The phase lock circuit according to any one of claims 3, 5 and 7 wherein said reference voltage generator means comprises oscillation means for oscillating a signal having a predetermined frequency, and a second phase comparator for comparing the phase of said input signal V_(IN) with the phase in the output signal of said oscillation means.
 24. The phase lock circuit according to any one of claims 4, 6 and 8 wherein said reference voltage generator means comprises oscillation means for oscillating a signal having a predetermined frequency, and a second phase comparator for comparing the phase of said input signal V_(IN) with the phase in the output signal of said oscillation means. 